There has recently been increasing demand for the incorporation of microcomputers that are capable of implementing high-level information processing into electronic equipment such as game machines, car navigation systems, printers, and portable information terminals. Such a thus-incorporated microcomputer is usually mounted on a user board called a target system. A software development support tool called an in-circuit emulator (ICE) is widely used for supporting the development of software to be used in the target system.
The CPU-switching type of ICE shown in FIG. 1 is the most common type of this kind of ICE used in the art. With this CPU-switching ICE, a microcomputer 302 is removed from a target system 300 during debugging, and a probe 306 of a debugging tool 304 is connected thereto instead. This debugging tool 304 emulates the operation of the removed microcomputer 302. The debugging tool 304 can also perform various processes necessary for debugging.
However, if the internal operating frequency of the microcomputer 302 of the CPU-switching ICE rises, it becomes difficult to obtain a real-time trace, due to delays in the signals generated by the probe 306 and the buffer that stores trace information.
In addition, if an attempt is made to store trace information in a trace buffer without limitations, the trace buffer would soon overflow so that it may not be possible to acquire trace information for the portions necessary for debugging. In such a case, it would be immensely convenient a trace range can be specified for collecting trace information therein. However, if the internal operating frequency of the CPU were to rise, it would become difficult to implement a trace range specification with external circuitry such as that of a CPU-switching ICE.
Systems are being developed to enable real-time tracing on a mass-produced chip, thus solving the above problems. In such a case, it is necessary to have a dozen or so dedicated terminals for transferring information over the address bus as trace information and storing it in real-time into a trace buffer. These terminals are necessary only during debugging, however, so they are useless as far as the end user is concerned and thus it is preferable to reduce them as far as possible.
In addition, it would also be extremely convenient to have a function that is capable of accurately acquiring trace information within a specified range, even during the implementation of a real-time trace on a mass-produced chip.